Kyung-Duk Zoh

Adsorption characteristics of selected hydrophilic and hydrophobic micropollutants in water using activated carbon

In this study, we investigated adsorption characteristics of nine selected micropollutants (six pharmaceuticals, two pesticides, and one endocrine disruptor) in water using an activated carbon. The effects of carbon dosage, contact time, pH, DOM (dissolved organic matter), and temperature on the adsorption removal of micropollutants were examined. Increasing carbon dosage and contact time enhanced the removal of micropollutants. Sorption coefficients of hydrophilic compounds (caffeine, acetaminophen, sulfamethoxazole, and sulfamethazine) fit a linear isotherm and hydrophobic compounds (naproxen, diclofenac, 2, 4-D, triclocarban, and atrazine) fit a Freundlich isotherm. The removal of hydrophobic pollutants and caffeine were independent of pH changes, but acetaminophen, sulfamethazine, and sulfamethoxazole were adsorbed by mainly electrostatic interaction with activated carbon and so were affected by pH. The decrease in adsorption removal in surface water samples was observed and this decrease was more significant for hydrophobic than hydrophilic compounds. The decline in the adsorption capacity in surface water samples is caused by the competitive inhibition of DOM with micropollutants onto activated carbon. Low temperature (5°C) also decreased the adsorption removal of micropollutants, and affected hydrophobic compounds more than hydrophilic compounds. The results obtained in this study can be applied to optimize the adsorption capacities of micropollutants using activated carbon in water treatment process.

Inactivation and UV Disinfection of Murine Norovirus with TiO2 under Various Environmental Conditions

ABSTRACT We studied inactivation and UV disinfection of murine norovirus (MNV) as a surrogate for human norovirus. We investigated the effects of different surface characteristics, temperatures, and NaCl concentrations on MNV survival using both a plaque assay and a real-time TaqMan reverse transcription (RT)-PCR assay. MNV survived more than 40 days on diaper material, on gauze, and in a stool suspension. Compared to inactivation at lower temperatures (−20 and 4°C), inactivation of MNV was greater at higher temperatures (18 and 30°C). On the surface of both gauze and diaper material, there was a <2-log10 reduction in the amount of infectious MNV in 40 days after incubation at both −20 and 4°C, compared to a >5-log10 reduction after incubation at 30°C in 24 days. MNV survived better in a stool suspension than on the surface of gauze or diaper material. A higher salt concentration increased the rate of inactivation of MNV. In 72 h, <0.3-, 1.5-, and 2.5-log10 reductions in the amount of infectious MNV occurred in distilled water and 0.5 and 1 M NaCl, respectively. We observed only minor reductions in the numbers of viral RNA copies as quantified by real-time TaqMan RT-PCR regardless of the temperature, the salt concentration, or the suspending medium. We also evaluated UV disinfection of infectious MNV with and without TiO2. The amount of MNV was significantly reduced by 254-nm UV with and without TiO2. When 25 mJ/cm2 UV was used, 3.3- and 3.6-log10 reductions in the amounts of infectious MNV occurred with and without TiO2, respectively. Our results demonstrate that MNV can persist in various environmental conditions and can be efficiently controlled by UV disinfection.

Kinetics and mechanism of photolysis and TiO2 photocatalysis of triclosan.

The degradations of triclosan (5-chloro-2-(2,4-dichlorophenoxy)-phenol), a potent broad-spectrum antimicrobial agent, were compared in TiO2-only in the dark condition, photolysis, and TiO2 photocatalysis with a UV-A lamp. TiO2 photocatalysis more effectively degraded and mineralized triclosan compared to TiO2-only and photolysis conditions. While triclosan removed only 30% by TiO2-only condition within 20 min, the triclosan degradation in photolysis and photocatalysis at the same time was 75 and 82%, respectively, and TOC removal was significantly higher in photocatalysis than in photolysis. The data of kinetics showed that triclosan adsorption onto TiO2 was fitted to Langmuir isotherm, and TiO2 photocatalysis was fitted to Langmuir-Hinshelwood model (b=27.99 mM(-1), K(triclosan)=9.49 mM(-1)). The neutral range of pH was favorable to photocatalysis due to the charge effect between TiO2 and triclosan. The addition of 2-propanol, a radical scavenger, significantly reduced the degradation of triclosan both in photolysis and photocatalysis. Dioxin-type intermediates such as dibenzo-dichloro-p-dioxin (DCDD), dibenzo-p-dioxin were produced in photolysis with and without 2-propanol, and also in photocatalysis with 2-propanol, but these intermediates were not detected in photocatalysis without 2-propanol. This result indicates that the photocatalytic degradation of triclosan is mainly achieved by radicals, and these radicals can further degrade dioxin-type intermediates once they are produced in photocatalysis.

A Fenton-like degradation mechanism for 1,4-dioxane using zero-valent iron (Fe0) and UV light

In this study, the degradation mechanism of 1,4-dioxane using zero-valent iron (Fe0) in the presence of UV light was investigated kinetically. The degradation of 1,4-dioxane in Fe0-only, photolysis, and combined Fe0 and UV reactions followed the kinetics of a pseudo-first-order model. The degradation rate constant (19 x 10(-4)min(-1)) in the combined reaction with UV-C (4.2 mW cm(-2)) and Fe0 (5 mg L(-1)) was significantly enhanced compared to Fe0-only (4.8 x 10(-4) min(-1)) and photolytic reactions (2.25 x 10(-4)min(-1)), respectively. The removal efficiency of 1,4-dioxane in combined reaction with Fe0 and UV within 4 h was enhanced by increasing UV intensity at UV-C region (34% at 4.2 mW cm(-2) and 89% at 16.9 mW cm(-2)) comparing with the removal in the combined reaction with Fe0 and UV-A (29% at 2.1 mW cm(-2), and 33% at 12.6 mW cm(-2)). It indicates that 1,4-dioxane was degraded mostly by OH radicals in the combined reaction. The degradation patterns in both Fe(0)-only and combined reactions were well fitted to the Langmuir-Hinshelwood model, implying that adsorption as well as the chemical reaction occurred. The transformation of Fe0 to Fe2+ and Fe3+ was observed in the Fe0-only and combined reactions, and the transformation rate of Fe0 was improved by UV irradiation. Furthermore, the reduction of Fe3+ was identified in the combined reaction, and the reduction rate was enhanced by an increase of UV energy. Our study demonstrated that the enhancement of 1,4-dioxane removal rate occurred via an increased supply of OH radicals from the Fenton-like reaction induced by the photolysis of Fe0 and H2O, and with producing less sludge.

Characteristics of trihalomethane (THM) production and associated health risk assessment in swimming pool waters treated with different disinfection methods

Swimming pool water must be treated to prevent infections caused by microbial pathogens. In Korea, the most commonly used disinfection methods include the application of chlorine, ozone/chlorine, and a technique that uses electrochemically generated mixed oxidants (EGMOs). The purpose of this study was to estimate the concentrations of total trihalomethanes (TTHMs) in indoor swimming pools adopting these disinfection methods, and to examine the correlations between the concentrations of THMs and TTHMs and other factors affecting the production of THMs. We also estimated the lifetime cancer risks associated with various exposure pathways by THMs in swimming pools. Water samples were collected from 183 indoor swimming pools in Seoul, Korea, and were analyzed for concentrations of each THM, TOC, and the amount of KMnO(4) consumption. The free chlorine residual and the pH of the pool water samples were also measured. The geometric mean concentrations of TTHMs in the swimming pool waters were 32.9+/-2.4 microg/L for chlorine, 23.3+/-2.2 microg/L for ozone/chlorine, and 58.2+/-1.7 microg/L for EGMO. The concentrations of THMs differed significantly among the three treatment methods, and the correlation between THMs and TTHMs and the other factors influencing THMs varied. The lifetime cancer risk estimation showed that, while risks from oral ingestion and dermal exposure to THMs are mostly less than 10(-6), which is the negligible risk level defined by the US EPA, however swimmers can be at the greater risk from inhalation exposure (7.77x10(-4)-1.36x10(-3)).

Wastewater treatment plants (WWTPs)-derived national discharge loads of perfluorinated compounds (PFCs).

The discharge of perfluorinated compounds (PFCs) was investigated for 15 wastewater treatment plants (WWTPs), comprising 25% of total domestic wastewater and 23% of total industrial wastewater produced in Korea. PFCs concentrations in influent, effluent, and sludge were greater in industrial wastewater than in the majority of domestic wastewater. Individual PFCs were found to have differing industrial sources, with perfluorocarboxylates used in fabric/textiles, paper-mill, and dyeing industries, and perfluoroalkylsulfonates occurring in oil/chemical and metal-plating/processing industries. Total WWTP-derived national discharge loads were calculated based on the average concentrations in effluents and the total volume of wastewaters produced in Korea. The average WWTP-derived national discharge loads of individual PFCs were 0.04-0.61 ton/year, with 63% of perfluorooctanoate being from domestic wastewater, and 75% of perfluorooctanesulfonate being from industrial wastewater. These estimates accounted for the majority of national emissions, based on measurements in major river mouths, indicating the major contribution of WWTPs to PFC occurrence in Korean aquatic environments. Both the per capita emission factor (μg/capita/day) for domestic discharge, and area-normalized national discharge loads (g/capita/km(2)/day) for all wastewaters were several factors lower in Korea than in Japan or Europe, which is consistent with the lower levels of human exposure to PFCs in Korea.

Fenton oxidation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX).

Oxidation of the high explosives hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1.3,5,7-tetrazocine (HMX) using Fentons reagent proceeds rapidly between 20 degrees C and 50 degrees C at pH 3. At an H2O2: Fe2+: RDX molar ratio of 5,178: 48: 1, RDX and HMX were completely removed in 1 to 2 h. All the experimental data could be fit to a pseudo first-order rate equation. The reaction rate was also strongly dependent on Fentons reagent concentrations. NO3- and N2 were identified as nitrogen byproducts from RDX and HMX oxidation. The experiment with radiolabeled RDX showed that approximately 37% of organic carbon in RDX was mineralized to CO2. We observed formaldehyde and formic acid as a short-lived intermediate. No other volatile or nonvolatile byproducts were found from GC/MS analysis. The results show that RDX and HMX can be effectively mineralized with Fentons reagents.

Occurrence and removal of selected micropollutants in a water treatment plant.

The levels of 14 micropollutants including nine pharmaceuticals, two pesticides, and three endocrine disruptors were measured in a water treatment plant (WTP) in Seoul, Korea. Among the measured micropollutants, 12 (excluding atrazine and triclocarban) were found in the influent and effluent from the WTP, at levels ranging from 2 to 482 ng L(-1). The removal efficiencies of the detected micropollutants in the WTP ranged from 6% to 100%. Among them diclofenac, acetaminophen, caffeine, carbamazepine, and 2,4-D were effectively removed (>80%). Metoprolol was unlikely to be removed (6%) in the WTP process. Concentrations of acetaminophen, metoprolol, ibuprofen, and naproxen were higher in winter, while levels of herbicides of 2,4-dichloro-phenoxyacetic acid (2,4-D) were higher in summer. Metoprolol was hardly removed in the water treatment process. Laboratory experiments showed that compounds with logKow>2.5 (especially bisphenol-A, 2,4-D, carbamazepine, triclocarban and 4-nonylphenol) were effectively removed by coagulation process, and adsorption effect increased in proportion with hydrophobicity of micropollutants and the turbidity of water. Sunlight photodegradation also effectively removed sulfamethoxazole, sulfamethazine, caffeine, diclofenac, ibuprofen, and acetaminophen, which are photosensitizes. Chlorination was relatively not effective for the removal of micropollutants due to the lower chlorine dosage (2 mg L(-1)), lower contact time (1h), and already lower levels of micropollutants at the chlorination stage at WTP. Our results imply that micropollutants during coagulation stage at WTP can be removed not only by coagulation itself, but also by adsorption to clay particle especially for high turbidity water, and by sunlight photodegradation in the areas open to the atmosphere.

Production of various disinfection byproducts in indoor swimming pool waters treated with different disinfection methods

In this study, the concentrations of disinfection byproducts (DBPs), including trihalomethanes (THMs; chloroform, bromodichloromethane, dibromochloromethane, and bromoform), haloacetic acids (HAAs; dichloroacetic acid and trichloroacetic acid), haloacetonitriles (HANs; dichloroacetonitrile, trichloroacetonitrile, bromochloroacetonitrile, and dibromoacetonitrile), and chloral hydrate (CH) were measured in 86 indoor swimming pools in Seoul, Korea, treated using different disinfection methods, such as chlorine, ozone and chlorine, and a technique that uses electrochemically generated mixed oxidants (EGMOs). The correlations between DBPs and other environmental factors such as with total organic carbon (TOC), KMnO(4) consumption, free residual chlorine, pH, and nitrate (NO(3)(-)) in the pools were examined. The geometric mean concentrations of total DBPs in swimming pool waters were 183.1±2.5μg/L, 32.6±2.1μg/L, and 139.9±2.4μg/L in pools disinfected with chlorine, ozone/chlorine, and EGMO, respectively. The mean concentrations of total THMs (TTHMs), total HAAs (THAAs), total HANs (THANs), and CH differed significantly depending on the disinfection method used (P<0.01). Interestingly, THAAs concentrations were the highest, followed by TTHMs, CH, and THANs in all swimming pools regardless of disinfection method. TOC showed a good correlation with the concentrations of DBPs in all swimming pools (chlorine; r=0.82, P<0.01; ozone/chlorine; r=0.52, P<0.01, EGMO; r=0.39, P<0.05). In addition, nitrate was positively correlated with the concentrations of total DBPs in swimming pools disinfected with chlorine and ozone/chlorine (chlorine; r=0.58; ozone/chlorine; r=0.60, P<0.01), whereas was negative correlated with the concentrations of total DBPs (r=-0.53, P<0.01) in the EGMO-treated pools.

Source apportionment of PM2.5 at the coastal area in Korea

In this study, we analyzed the chemical composition of fine particulate matter 2.5 μm or less (PM) collected at Incheon, the coastal area in Seoul, Korea every third day from June 2009 to May 2010. Based on the analyzed chemical species in the PM samples, the sources of PM were identified using a positive matrix factorization (PMF). Nine sources of PM were determined from PMF analysis. The major sources of PM were secondary nitrate (25.4%), secondary sulfate (19.0%), motor vehicle 1 (14.8%) with a lesser contribution from industry (8.5%), motor vehicle 2 (8.2%), biomass burning (6.1%), soil (6.1%), combustion and copper production emissions (6.1%), and sea salt (5.9%). From a paired t-test, it was found that yellow sand samples were characterized as having higher contribution from soil sources (p<0.05). Furthermore, the likely source areas of PM emissions were determined using the conditional probability function (CPF) and the potential source contribution function (PSCF). CPF analysis identified the likely local sources of PM as motor vehicles and sea salt. PSCF analysis indicated that the likely source areas for secondary particles (sulfate and nitrate) were the major industrial areas in China. Finally, using the source contribution of PM and associated organic composition data, principal component analysis (PCA) was conducted to evaluate the accuracy of the PM source apportionments by PMF. The PCA analysis confirmed eight of the nine PM sources. Our result implies that the chemical composition analysis of PM data and various modeling techniques can effectively identify the potential contributing sources.